Triumphrat

tealetm · 05-31-2007, 09:51 PM

So I was thinking the other day- what's the purpose of a radiator fan staying on after a car/motorcycle is shut off?

I went out a few weeks ago on a hot day, and the fan kicked on as I was pulling up to my apartment. After I shut the engine off, the rad. fan kept going. This obviously happens on cars and bikes.

Anyway- whats that point of this? When the engine is shut off, the water pump is no longer turning- meaning the coolant the fan is cooling does not cycle through the engine- meaning the engine isn't cooling anymore than w/o the fan.

What gives?

Jhumphrey · 06-01-2007, 06:40 AM

Probably just trying to prevent loosing coolant from the system.

RexxyPup · 06-01-2007, 07:17 AM

I'm guessing, but the block is significantly hotter than the water, hence the actual heat transfer process. So turn off your engine and the water in the engine jacket continues to heat up for some time, but the impetus (other than convection flow which will be quite slow) to move the hot coolant to the radiator has gone.

keep the fan on, and you keep the coolant temp gradient high enough to keep the water flowing round and remove the remaining heat in the block, without perhaps local boiling?

Rexx

Cuyose · 06-02-2007, 10:18 PM

I was wondering this too the other day, but it makes sense that it would go on and cool whats in the radiator, as a hot engine and 211 degree coolant would quickly start boiling and fill your resevior very quickly.